Remove "\n" from echo argument. echo does not support escape sequences.

contrib/gitian-build.sh

@@ -105,7 +105,7 @@ while :; do
 		fi
 		shift
 	    else
-		echo 'Error: "--os" requires an argument containing an l (for linux), w (for windows), or x (for Mac OSX)\n'
+		echo 'Error: "--os" requires an argument containing an l (for linux), w (for windows), or x (for Mac OSX)'
 		exit 1
 	    fi
 	    ;;